Zebra Mussels (Dreissena polymorpha) are an invasive freshwater mussel species originally native to the Caspian Sea, Black Sea, and their tributaries in Eastern Europe. They were introduced to North America in the 1980s, most likely through ballast water from transoceanic ships. Since their discovery in the Great Lakes in 1988, they have rapidly spread across freshwater systems in the United States and Canada, profoundly affecting ecosystems, infrastructure, and water quality.
Identification and Characteristics
• Scientific Name: Dreissena polymorpha
• Size: Small, typically 2-3 cm (0.8-1.2 inches) in length, though some may reach 5 cm (2 inches).
• Appearance:
• Shell Shape: Triangular with a flattened underside, allowing them to sit on their edge.
• Pattern: Black, brown, or cream-coloured shells with a distinct zigzag striped pattern, though the colouration may vary.
• Life Span: Typically 2-5 years.
Habitat
• Depth: Found in shallow to moderately deep waters, generally up to 30 metres (98 feet).
• Water Conditions:
• Prefers nutrient-rich freshwater with moderate to high calcium levels for shell production.
• Thrives in temperatures between 10-25°C (50-77°F), though they can survive in a wider range.
• Substrate: Attaches to hard surfaces like rocks, docks, boat hulls, intake pipes, and even other mussels.
Introduction and Spread in North America
• Pathway:
• Zebra mussels were introduced to North America in the 1980s, likely via ballast water from ships entering the Great Lakes from Eastern Europe.
• First discovered in Lake St. Clair in 1988, they quickly spread to all of the Great Lakes and have since invaded many inland lakes and rivers.
• Mechanism of Spread:
• Zebra mussels produce free-floating larvae called veligers, which can be transported via currents, ballast water, or water equipment.
• They also spread by attaching to boats, trailers, and gear, hitchhiking into new waterways.
Ecological Impact
1. Disruption of Ecosystems
• Zebra mussels are filter feeders, capable of filtering 1 litre of water per day per mussel.
• This removes plankton, which is a vital food source for native fish and aquatic species, disrupting food chains.
• Their filtration can improve water clarity, which may seem beneficial but often leads to algal blooms, including harmful blue-green algae.
2. Colonization and Outcompetition
• Zebra mussels form dense colonies, smothering native mussels, crayfish, and other aquatic species.
• Their aggressive colonization displaces native species, reducing biodiversity.
3. Impact on Aquatic Life
• The mussels excrete phosphorus and nitrogen, altering water chemistry and promoting algal growth.
• Sharp mussel shells littering lakebeds can harm fish, birds, and other species.
Economic Impact
1. Infrastructure Damage
• Zebra mussels clog water intake pipes, cooling systems, and hydroelectric plants, leading to costly maintenance.
• Colonization of docks, marinas, and buoys requires frequent cleaning and repair.
2. Tourism and Recreation
• Beaches become littered with sharp shells, creating hazards for swimmers.
• Decaying mussels release a foul odour, diminishing the appeal of recreational areas.
3. Cost of Management
• The annual economic impact of invasive mussels in North America is estimated to be in the billions of dollars, with significant resources allocated to prevention, cleanup, and repair.
Control and Management
1. Prevention
• The most effective way to manage Zebra mussels is to prevent their spread:
• Clean, Drain, and Dry:
• Clean all boats, trailers, and gear of visible mussels or plants.
• Drain water from bilges, live wells, and engines.
• Dry equipment thoroughly before using it in another waterway.
• Inspect boats and other equipment before launching in new waters.
2. Chemical Controls
• In closed systems like water treatment plants, chemical treatments like chlorine or potassium chloride are used to control mussel populations.
3. Biological Research
• Efforts are underway to identify natural predators or pathogens that can target Zebra mussels without harming native species.
4. Monitoring and Public Awareness
• Organizations such as Stop Aquatic Hitchhikers! and Invasive Species Centres provide resources and educational campaigns to increase public awareness of the problem.
Zebra Mussels vs. Quagga Mussels
Characteristic
Zebra Mussels
Quagga Mussels
Shape
Flattened underside; sits on edge.
Rounded underside; sits flat.
Habitat
Prefers hard surfaces in shallower waters.
Can colonize hard and soft substrates, including deeper waters.
Environmental Range
Thrives in warmer, nutrient-rich waters.
More adaptable to cooler, nutrient-poor environments.
Dominance
Often displaced by Quagga mussels.
Outcompetes Zebra mussels in many regions.
Presence in Skaneateles Lake
• Zebra mussels have been documented in Skaneateles Lake, often colonizing underwater structures like rocks, boats, and wrecks.
• Their presence has contributed to changes in water quality, including increased clarity and altered nutrient cycling, which can affect native species.
• These mussels are frequently found alongside Quagga mussels, with both species competing for dominance in the lake.
Further Resources
1. Invasive Species Centre
• https://www.invasivespeciescentre.ca
• Offers tools, guidelines, and resources for managing Zebra mussels in Canada.
2. U.S. Geological Survey (USGS) Nonindigenous Aquatic Species Database
• Tracks the spread of Zebra mussels in North America.
3. Finger Lakes Institute
• Focuses on invasive species management in the Finger Lakes region, including Zebra mussels.
Conclusion
Zebra mussels are a highly invasive and destructive species that have reshaped ecosystems and economies across North America, including Skaneateles Lake. Their ability to rapidly colonize new habitats and disrupt ecosystems makes them a significant challenge for conservationists, divers, and recreational lake users. While prevention and management efforts are ongoing, the fight against Zebra mussels highlights the importance of public awareness and coordinated action to protect freshwater systems from further invasion.